It is commonplace, in the manufacture of a wide variety of electronic and/or fabricated metal parts require spot welds to weld together two metals, and frequently metals which are dissimilar to each other. One of the difficulties that has been incurred by the prior art in welding such metals is the inability to accurately control the power used in the welding operation and hence the quality of the weld itself. It has been proposed, as described in U.S. Pat. Nos. 4,019,364, 4,392,044 and 5,298,711, to either evaluate the quality of a weld or to control the welding operation using the welded part as a thermocouple.
The techniques as described in the afore-mentioned patents suffer from the disadvantage of not being suitable to both control and evaluate in the same operation the welding process.
It is accordingly an object of the present invention to provide a new and improved method for the welding of metals using the thermo-electricity output of the metals being welded to both control and evaluate the welding process.
It is a related object, of the present invention to provide a method for the welding of metals in which the weld current is optimized using the resistance of the metals being welded and the rate of cooling of the metals being welded as a measure of the mass of the metals.
It is a more specific object of the invention to provide a method for the welding of metals in which an initial pulse of current is applied to the metals being welded to enable the resistance of the metals to be calculated and to enable the mass of the metals to be determined by the rate of cooling of the metals for use in the determination of the necessary welding energy required to effectively weld the metals.
It is yet another object of the invention to provide a method for the control and evaluation of the welding of metals in which the rate of cooling of the welded metals is used to evaluate the quality of the weld.